Diesel engines operate by compressing air, including oxygen, within a combustion chamber with a piston, and then injecting fuel, which includes hydrocarbons, into the compressed air. Because the air heats up during compression, the fuel ignites upon being injected into the compressed air.
Some failure modes of various components of diesel engines, such as a turbocharger, may introduce hydrocarbons into the flow of air provided to an intake manifold, which are then circulated into the combustion chamber and combusted. Alternatively, a fuel injection system may malfunction and remain stuck open, continuing to inject fuel into the combustion chamber. Some other conditions may also result in uncontrolled hydrocarbon introduction into the combustion chamber. These other conditions may include but are not limited to an over-dose of starting fluid, overfill of engine lubrication oil, or severe lubrication oil/fuel dilution. These hydrocarbon based contaminants may allow the diesel engine to continue operating even after the controlled fuel supply to the engine is disengaged. This situation may lead to the diesel engine continuing to accelerate in rotational speed, and may be referred to as a “runaway” situation.